Coated rolls are used in paper machines and in paper finishing devices in substantially different applications. As examples of such applications, soft rolls for soft calenders and supercalenders, and equivalent, should be mentioned. Usually the soft coatings on rolls are made of organic polymers or mixtures thereof, which often also include inorganic elements. The soft coatings on rolls are often made of a composite structure, which comprises layers made of different materials.
In calenders, such as soft calenders or supercalenders, the roll nips are so-called soft nips, i.e., nips in which a hard roll is fitted as a pair with an elastically resilient roll. Elastically resilient rolls have been so-called paper-filled rolls, i.e., rolls that consist of paper strips fitted as layers one above the other, but at present various types of polymer-coated rolls are used more and more commonly as the resilient rolls.
The coating on a polymner-coated roll is an insulator, and when the roll revolves, the polymer coating produces thermal energy as a result of the nip effect and as a result of compression and bending, and this thermal energy is partly conducted into the metal-mantle frame of the roll. The surface temperature of the polymer can be up to about 80.degree. C. during calendering. The metal mantle of the roll expands because of the thermal energy, which also affects the quality of the paper to be calendered. From the roll mantle, heat is also conducted to the roll ends and to the shafts, which are not placed inside the insulating polymer coating, in which connection a difference in temperature arises between the middle portions and the lateral portions of the roll, as a result of which the roll becomes distorted and somewhat "barrel-shaped". This phenomenon is not desirable in view of the calendering process or of the use of the coatings, in particular in view of their service life.